Generally, RTK positioning is the one method of interferometric positioning measurable in a short time. In this method, integral-value bias is determined at the time of an observation start (initialization), observational data is communicated between receivers, and this observational data performs analysis processing on real time. Thus, in RTK positioning, high precision positioning is performed moving and it is applied to the position control of movable bodies, such as a pilotless plane and a car.
Even if the number of satellites which can be caught increases in the positioning using the satellite in the urban canyon, when low elevation angle and signal strength are low, a positioning signal is judged with the mask threshold of an elevation mask or a signal strength mask (C/N0 mask) to be a big signal of a multipath error, and these satellites are not used in positioning calculation.
Generally, if a positioning signal is strongly influenced by a multipath error, signal strength will fall greatly. Then, there are the GPS receiving device and correcting method which can amend the measuring point of a mobile station by distinguishing simply and certainly the satellite signal influenced by the multipath. This correcting method is disclosed by WO 2006/132003 (patent document 1), and be shown in FIG. 5, if a satellite signal is received (step 100), the data for position correction of reference station and the reception intensity of the satellite signal in reference station will be calculated (step 110), the reception intensity of the satellite signal in a mobile station, and the delta pseudo range/delta pseudo range rate of change of a mobile station are calculated (step 120), and the reception intensity of the satellite signal in the reference station and a mobile station is compared, when the difference of the reception intensity is more than predetermined threshold T1, and when a delta pseudo range/delta pseudo range rate of change is more than predetermined threshold T2, the satellite signal of the satellite is excepted from the satellite signal for positioning, and positioning accuracy is raised. If it puts in another way, when the difference of the reception intensity of the satellite signal in a reference station and a mobile station>=T1 and the delta pseudo range/delta pseudo range rate-of-change>=T2, the satellite signal of said satellite will be excluded from the satellite signal for positioning, and positioning accuracy will be raised.
In “The Effect of Terrian Mask on RAIM Availability, T. Radisic, et al, Journal of Navigation, 2010” (non-patent document 1), the RAIM forecasting method which took the influence of the altitude by surrounding geographical feature into consideration is used. In this RAIM forecasting method, a present receiver position and present satellite information are searched for from the database of DEM (numerical Elevation Model), this data is used, an elevation mask is changed according to the altitude of geographical feature, and the Dilution Of Precision value is evaluated.
In “Increasing GNSS RTK availability with a new single-epoch batch partial ambiguity resolution algorithm, Parkins A, GPS Solutions, 2010” (non-patent document 2), in consideration of the combination of all the satellites in a visible range, the satellite with which the solution of a Ratio test becomes best in the combination of all the satellites is chosen.